PHYSIOLOGY OF ANIMAL HEAT. 



SOURCES OF HEAT. 



The heat of the body is a form of kinetic energy appearing without 

 interruption and must be conceived as depending upon vibrations of 

 the atoms of the body. In the last analysis every source of heat is 

 contained in the mass of potential energy taken into the body as food, 

 in combination with the oxygen obtained from the air in the act of 

 respiration. The amount of heat liberated depends upon the amount of 

 potential energy transformed. 



The potential energy of nutrient matters may be appropriately desig- 

 nated as latent heat, inasmuch as it may be conceived that in their 

 consumption in the body, which is essentially a process of combustion, 

 kinetic energy is transformed only in the form of heat. As a matter of 

 fact, mechanical energy and electricity are also developed from the 

 potential energy supplied. However, in order to obtain a uniform 

 measure for the forces transformed, it is advisable to express all potential 

 energy in terms of heat-units. The calorimeter is an apparatus with the 

 aid of which the amount of potential energy contained in food-stuffs 

 can be converted experimentally into heat and the units of the latter 

 can at the same time be measured. 



Favre and Silbermann employed the so-called water-calorimeter (Fig. 133). 

 A cylindrical box, the so-called combustion-chamber (K), serves for the recep- 

 tion of the substance to be burned. This box is suspended in a larger, cylindrical 

 vessel (L), which is filled with water (w), so that the combustion-chamber is 

 completely surrounded thereby. Three tubes enter into the upper portion of 

 the chamber: one (O) is intended for the passage of air containing oxygen, 

 which is necessary in the process of combustion. The second tube (a) in the 

 middle of the cover is closed above with a thick glass plate, upon which is mounted 

 at an angle a mirror (s) , which permits the observer (B) to look into the interior 

 of the chamber from a lateral point of view in the direction b b. in order to observe 

 the process of combustion at c. The third tube (d) is employed only when it 

 is desired to consume combustible gases in the chamber and through it these 

 are then passed. Generally this tube is closed by a cock. A lead pipe (e e) also 

 passes out of the upper portion of the chamber and in a convoluted arrangement 

 traverses the volume of water, finally reaching the surface at g. Through this 

 the gases of combustion escape, being cooled in the convoluted tube to the tem- 

 perature of the water. 



The cylindrical vessel containing the water is covered with a lid having open- 

 ings for the four tubes that pass through it. The water-cylinder stands upon 

 legs within a larger cylinder (M), which is filled with a poor conductor of heat. 

 Finally this is placed in a still larger cylinder (N), which again contains water 

 (W) . This last layer of water is intended to prevent any heat from the exterior 

 from raising the temperature of the water in the interior. A definite amount of 

 the material to be examined is burned in the combustion-chamber. After com- 

 bustion has been completed, during the progress of which the water in the interior 

 is repeatedly stirred, the temperature of the water is determined by means of a 

 delicate thermometer. If the amount of increase in temperature is noted, and 

 if the amount of water in the inner cylinder is known, the number of heat-units 

 furnished by the combustion of the measured amount of the substance under 

 examination can be readily estimated. 



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